1. Field of the Invention
The present invention relates to a method and apparatus for detecting and compensating inclination of an objective lens, and more particularly to a method and apparatus for detecting and compensating inclination of an objective lens that is capable of accurately discriminating inclination of an objective lens inside an optical pick-up caused due to an eccentricity of an optical disk and other factors and quickly coping with it.
2. Description of the Background Art
Generally, an optical disk driving apparatus reads a data recorded in an optical disk by means of an optical pick-up, processes the read signal and releases its compression, to thereby implement an image and an audio.
When a tracking and focussing servo operations are turned on, the optical pick-up beams laser on a predetermined position of the optical disk and picks up the reflected light to read a data.
When the data is read from the optical pick-up, a problem may arise that the objective lens of the optical pick-up is inclined from an optical axis to a side due to an eccentricity of the optical disk or other factors.
In order to solve the problem, a GFS (Good Frame Sync) signal is used in the optical disk driving apparatus.
When the rotation rate of the optical disk reaches a predetermined rate, a synchronous signal of a frame is detected at predetermined time intervals, that is, periodically. The GFS signal is a signal outputted as a high level in case that the periodically detected synchronous signal is as many as a predetermined number consecutively within a predetermined time, which is also utilized to check the eccentricity of the optical disk.
FIG. 1 illustrate wave forms indicating an center error signal and the GFS signal generated when the objective lens is stable, of which the first wave form indicates a sled compensation signal, the second wave form indicates a tracking servo signal, the third wave form indicates a center error signal and the fourth wave form indicates the GFS signal.
The center error signal is a signal to control the objective lens for axial center not to deviate when the track is searched, that is, when the optical pick-up jumps from the currently reproducing point to other point.
As shown in the center error signal wave form, when the objective lens continuously follows the track of the optical disk without inclination, the GFS signal maintains a high level.
FIG. 2 illustrates wave forms of a center error signal and a GFS signal generated when the objective lens is inclined to a side when the objective lens is switched from a reproduction operation to a searching operation or other factors such as a search due to a scratch or a dust of the disk. In this drawing, it is noted that the GFS signal is abnormally outputted.
FIG. 3 illustrates wave forms of signals according to the process that the objective lens returns to the optical axis. In this drawing, a controlling operation is performed to check the GFS signal of FIG. 2 and return the servo to its original state, but as soon as the servo returns to the original state, the lens is inclined again and a long time (a few seconds) is taken for the object lens to return to its original state.
As shown in the wave form of the center error signal, in case that the objective lens is inclined to one side, the center error signal is not constant, and the GFS signal is not normally outputted. With the GFS signal outputted as such, the objective lens is judged to be in an inclined state, according to a compensation operation is performed.
However, besides the case where the objective lens is inclined, there may occur that the GFS signal is not normally generated and is maintained at a low level.
That is, in case that the objective lens is inclined from the optical axis to a side, in case that the disk is not in a good state or in case that the speed of a spindle motor is not normally controlled, the GFS signal has the low value and the data reading from the optical disk is not normally performed.
Therefore, it is not possible to discriminate with the GFS signal whether it falls to the case that the objective lens is inclined or the disk is in a bad condition.
Thus, in the conventional art, if the GFS signal is not normally outputted, first, it is judged that the disk is in a bad condition, so that the optical pick-up is moved to a different position of the optical disk and performs data reading.
After the optical pick-up is moved, as shown in FIG. 3, if the GFS signal does not return to a high level signal, that is, if the lens does not return to the center and maintains the inclined state even through the optical pick-up is moved to a difference position and performs reading, it is judged that the objective lens has inclined, so that the spindle motor for rotatably driving the optical disk is stopped from driving and the processes are re-performed from the automatic focussing operation.
The center error signal are shown in FIG. 1 or 3 to indicate the degree of inclination of the center of the objective lens, which is not taken into consideration in case of normal reproducing operation in the conventional system, and which is illustrated to show characteristic of each signals.
The above processes will now be described with reference to FIG. 4.
FIG. 4 is a flow chart of the method for detecting inclination of an objective lens.
First, the optical disk is inserted (S10) and a tracking servo and a focus servo is turned on (S11). While the optical disk is being reproduced, it is checked whether the GFS signal is normally outputted (S12). When the GFS signal is normally outputted, that is, when the GFS signal is maintained at a high level, the optical disk keeps reproducing, while if the GFS signal is outputted as a low level signal for a predetermined time (T1) (S14), it is judged that the disk is in a bad condition, so that the optical pick-up is moved to a different position of the optical disk to read a data of the position (S17). If the low level signal is continuously detected (S16) for a predetermined time (T2) even after the optical pick-up is moved, it is judged that the objective lens has inclined from the optical axis to a side, so that the spindle motor is stopped and the processes are attempted again from the automatic focussing operation (S18).
However, the conventional art is disadvantageous in that in case that the objective lens has inclined from the optical axis to a side, only when the GFS signal is outputted as a low level signal for a predetermined time, the objective lens is judged to have inclined and operated, causing an unnecessary delay of time.
In addition, in the case that the lens has inclined to one side, even through the sled servo is compensated as far as the inclined distance, the lens may not return to the center.
Therefore, an object of the present invention is to provide a method for detecting inclination of an objective lens in which, in order to detect inclination of an objective lens inserted in an optical pick-up, inclination of an objective lens is quickly and accurately detected in consideration of a GFS signal and a center error signal generated by the rotation of an optical disk, thereby making a normal reproduction within a short time, and its apparatus.
Especially, in the method for detecting inclination of an objective lens of the present invention, the center error signal, which is generally used to control the center of the objective lens in searching a track, is utilized for a normal reproduction, thereby compensating inclination of the objective lens quickly.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for detecting inclination of an objective lens including the steps of: initially driving an optical disk and detecting a record signal while travelling on the track of the optical disk; checking whether a GFS signal according to the rotation of the optical disk is normally detected; checking a center error signal value outputted from the optical pick-up which reads a record data on the optical disk in case that the GFS signal is abnormally detected; and discriminating inclination of the objective lens on the basis of the checked center error signal value, thereby judging inclination of the objective lens quickly and accurately.
To achieve the above objects, there is also provided an apparatus for detecting inclination of an objective lens including: an optical pick-up for reading a data recorded on the optical disk; a spindle motor for rotating the optical disk; a sled motor for moving the optical pick-up horizontally; a drive unit for driving the spindle motor and the sled motor; a center error signal detector for detecting a center error signal from an output signal of a photodiode inserted in the optical pick-up; an A/D converter for converting the signal outputted from the center error signal detector to a digital signal; an RF unit for generating a servo error signal and a reproduction RF signal according to the signal read by the optical pick-up; a digital signal processor for outputting a reproduction data according to the signal outputted from the RF unit, controlling the drive unit and outputting a GFS signal; and a microcomputer for judging whether the objective lens inserted in the optical pick-up has inclined according to the GFS signal outputted from the digital signal processor and the center error signal outputted from the A/D converter, and accordingly performing a compensation operation.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.